Metal corrosion is a phenomenon where metal elutes or a corrosion product is precipitated due to chemical reaction (oxidation-reduction reaction) that occurs between metal and water interface. Metal is widely used not only in familiar products such as household appliances, but also in machine parts and building structures. Metal corrosion causes deterioration in function and performance of such artificial products, and is one of major problems that prevent long-term stable use. Thus, researches related to the occurrence mechanism of corrosion and the development of effective anticorrosion techniques have been conducted for a long time.
Actual metal corrosion phenomena progress over the years, i.e., over several years to several tens of years. It has been therefore difficult to find corrosion pitting in a short period of time. Thus, there has been employed a test method of measuring a crevice corrosion depth and a pitting depth by immersing a metal in the same corrosive liquid as that under the usage environment such as seawater for one year or more. Under the circumstances, a prediction technique of a metal corrosion rate that enables the prediction of a corrosion progress level in a short period of time has been demanded.
As a prediction technique of metal corrosion/anticorrosion problems, PTL 1 discloses a method of using polarization curve data. Since an actual polarization curve changes with time, PTL 1 discloses a method of measuring an actual surface potential or current density, and obtaining a polarization curve using the measured value to estimate a polarization curve obtainable after the lapse of a certain period of time.
In addition, PTL 2 discloses a device for evaluating the potential of a sacrificial anticorrosion metal. The device includes a means for cooling and heating a corrosive liquid and a means for spraying the corrosive liquid onto a test piece. The device further includes a means for adjusting a crevice portion and a means for measuring the potential of the test piece via a standard electrode.
In addition, PTL 3 discloses a method of measuring the surface potential and the weight change of a metal to obtain the correlation existing between the surface potential and the corrosion amount of the metal, and quantitatively evaluating a corrosion amount from the measured surface potential on the basis of the obtained correlation.